1. Field of the Invention
This invention relates to a hidden-mark observing apparatus that observes the hidden marks of a lens to be examined (hereinafter referred to as a subject lens), particularly, of a progressive power lens (i.e., varifocal lens) and relates to a lens-meter that is capable of observing these hidden marks.
2. Description of the Related Art
In general, there are painted marks and stamped marks on the surface of an unprocessed progressive power lens. From a painted mark, the lens maker, lens type, and the distance portion and near portion positions of the lens can be identified. Therefore, when the power of an unprocessed progressive power lens is measured by, for example, a lens-meter, the measurement can be performed at the marked position. However, if once an unprocessed lens is processed and the framing is completed, the painted mark will be wiped off by alcohol and the like and therefore it will be very troublesome to investigate the addition power of the framed progressive power lens even by the use of a latest lens-meter with a progressive measuring function.
On the other hand, the hidden mark stamped on the progressive power lens surface includes the lens' geometrical center position, added lens power, and so on, in addition to the lens maker and the lens type. Therefore, if the stamped mark is deciphered, the added lens power, etc., can be identified.
However, the hidden mark is a very shallow stamp so that it does not become a hindrance when actually used. For this reason, in order to perform the specification or decipherment of the hidden mark position, the hidden mark is held before a fluorescent light, or the reflection at a shallow angle is viewed. However, there is a problem in that the discovery and decipherment of hidden marks are very difficult for an unskilled person.